1. Field of the Invention
The present invention relates generally to a measuring system for measuring a field of view (FOV) of digital camera modules and, more particularly, to a FOV measuring system that simplifies measuring procedures.
2. Description of Related Art
Digital cameras are now in widespread use with the ongoing development of micro-circuitry and multimedia technologies. High-end portable electronic devices, such as mobile phones and personal digital assistants (PDAs), are being developed to be increasingly multi-functional. Many of these portable electronic devices are now equipped with digital camera modules.
In a digital camera module, a FOV is a very important factor in determining the quality of the pictures captured by the digital camera module. Therefore, the FOV of the digital camera module requires measuring before the digital camera module is deemed acceptable for use.
Referring to FIG. 1 and FIG. 2, a digital camera module 50 includes a lens module 501 and an image sensing module 503. When the FOV θ of the digital camera module is measured, the digital camera module 50 is used to image a measuring chart 20. The lens module 501 captures an image area 201 of the chart 20 and forms an object image 201′ on the image sensing module 503. The FOV θ can be described by either equation 1 or equation 2 below:θ=2×arc tan(d/2s)  (Equation 1)θ=2×arc tan(d′/2f)  (Equation 2)Wherein d is a length of a diagonal line AC of the image area 201, d′ is a length of a diagonal line A′C′ of the image area 201′, s is a distance between the lens module 501 and the measuring chart, and f is a focal length of the lens module 501. The image sensing module 503 is placed in an image plane of the lens module 501, and, therefore, a distance between the image sensing module 503 and the lens module 501 is equal to the focal length f of the lens module 501.
In this way, if d and s are measured, the FOV θ can be calculated using equation 1; if d′ and f′ are measured, the FOV θ can be calculated using equation 2.
Referring to FIG. 3, a typical FOV measuring system 100 is used to measure a FOV of a digital camera module 50. The typical measuring system 100 includes a measuring chart 20, a parameter inputting module 30, and a processing module 40. The digital camera module 50 includes a lens module 501 and an image sensing module 503. The lens module 501 captures an image area 201 of the chart 20 and forms an object image 201′ on the image sensing module 503. The image sensing module 503 converts optical signals of the object image 201′ into electrical signals and transmits the electrical signals to the processing module 40. The parameter inputting module 30 inputs a pixel length Ld of each pixel of the image sensing module 503 and a distance f between the lens module 501 and the image sensing module 503 into the processing module 40. At the same time, the processing module 40 calculates the number of pixels Pd of a diagonal A′C′ of the image area 201′ by means of automatically searching a frame of the measuring chart 20. In this way, the FOV θ can be calculated by means of the equation 2:θ=2×arc tan(d′/2f)=2×arc tan(Pd×Ld/2f)
However, much time is needed in searching a boundary of the image area 201, and the processing module 40 is prone to make mistakes in such an automatic search. Additionally, when the typical measuring system 100 is used to measure different types of digital camera modules 50 with different pixel lengths Ld, the pixel length Ld of each type of digital camera module 50 requires measuring and inputting into the processing module 40. This work costs more time and manpower.
Therefore, a new system for measuring FOV of camera modules and a new measuring method are desired in order to overcome the above-described shortcomings.